Friction is the major factor that resists motion of objects in fluids of any type. About any object that moves in water, there is a motionless layer of water, called "boundary-layer". The water in this layer is motionless because of the extremely high shear forces experienced by it. For a given fluid viscosity, (which is a function of temperature), the faster the object moves in it, the thinner the boundary-layer becomes. The change is accompanied by intensification of the shear forces within the layer. Because these forces interact with the water flowing relative to the moving object, the overall resistance of the water to the object's advancement increases.
Objects designed for high advancement rates in water, (e.g. torpedoes) are configured to form about them laminar water flow patterns. These patterns are conducive to easier advancement. Objects with shapes and/or surfaces which create turbulent water flow patterns about themselves encounter more severe water resistance. The effects of torpedoes' shapes and surfaces on water resistance to their advancement rate is mentioned in here for background information only. Substantial work was and is conducted in the area of torpedoes' optimized configurations. This invention does not deal with the subject.
The present invention deals only with reduction of resistance of water to motion of torpedoes through alteration of the motionless "boundary-layer" and its close vicinity.
Attempts have been made in the prior art to disturb the boundary layer through controlled discharges of water jets, air bubbles, or oil. These attempts have met with differing but unpublished degrees of success.
In the U.S. patent of Lee, U.S. Pat. No. 3,041,992, issued July 3, 1962, a cone is projected in advance of the nose of a torpedo for the purpose of creating a cavitation bubble in which the torpedo may more effortlessly travel. At column 2, lines 24-31 modulation of the spatial orientation of the cavitation bubble is described as a means for steering the torpedo.
There exist recognitions in the prior art that vibrations induced at or near the surface of a body that is travelling through a fluid medium can be used to break up the boundary layer, aid in shedding vortices, and to cancel-out unwanted vibrations.
Caddell, U.S. Pat. No. 3,008,673, issued Nov. 14, 1961 provides a bridge between the problem of moving an airfoil through the air and moving a hydrofoil through a liquid medium such as water.
Some of the prior art relates to the problem of easing the flow of a fluid through a tubular structure. Bodine, Jr., U.S. Pat. No. 2,853,852, issued Sep. 30, 1958 provides an example, as does Smith, U.S. Pat. No. 3,099,993, issued Aug. 6, 1963.
Bodine, Jr., also has an earlier U.S. Pat. No. 3,783,008, which relates to easing the passage of a wing through the air. Thus, there is some appreciated analogy in the prior art between slipping fluid through a tube and slipping an object through a fluid.
Ellis, Jr., U.S. Pat. No. 2,899,150, issued Aug. 11, 1959, Quinn, U.S. Pat. No. 3,774,867, issued Nov. 27, 1973 and Poisson-Quinton, U.S. Pat. No. 2,585,676, issued Feb. 12, 1952, are further examples of a wing drag reduction by boundary air layer disturbance. A related problem is treated in Maurer, U.S. Pat. No. 3,934,846, issued Jan. 27, 1976: how to reduce drag and vibration caused to an aircraft, e.g. a bomber, when a cavity, such as a bomb bay is opened.
The use of controlled electromagnetic radiation at the nose cone of a re-entering space vehicle to cause a shedding of a plasma layer, as is described in Hoff, U.S. Pat. No. 3,224,375.